AMD isn't only getting back in the game on processors - they also just finally truly unveiled Vega, the new line of Radeon graphics cards. AnandTech benchmarked the two cards, and concludes:

Unfortunately for AMD, their GTX 1080-like performance doesn't come cheap from a power perspective. The Vega 64 has a board power rating of 295W, and it lives up to that rating. Relative to the GeForce GTX 1080, we've seen power measurements at the wall anywhere between 110W and 150W higher than the GeForce GTX 1080, all for the same performance. Thankfully for AMD, buyers are focused on price and performance first and foremost (and in that order), so if all you’re looking for is a fast AMD card at a reasonable price, the Vega 64 delivers where it needs to: it is a solid AMD counterpart to the GeForce GTX 1080. However if you care about the power consumption and the heat generated by your GPU, the Vega 64 is in a very rough spot.

On the other hand, the Radeon RX Vega 56 looks better for AMD, so it's easy to see why in recent days they have shifted their promotional efforts to the cheaper member of the RX Vega family. Though a step down from the RX Vega 64, the Vega 56 delivers around 90% of Vega 64’s performance for 80% of the price. Furthermore, when compared head-to-head with the GeForce GTX 1070, its closest competition, the Vega 56 enjoys a small but none the less significant 8% performance advantage over its NVIDIA counterpart. Whereas the Vega 64 could only draw to a tie, the Vega 56 can win in its market segment.

Vega 56's power consumption also looks better than Vega 64's, thanks to binning and its lower clockspeeds. Its power consumption is still notably worse than the GTX 1070's by anywhere between 45W and 75W at the wall, but on both a relative basis and an absolute basis, it's at least closer. Consequently, just how well the Vega 56 fares depends on your views on power consumption. It's faster than the GTX 1070, and even if retail prices are just similar to the GTX 1070 rather than cheaper, then for some buyers looking to maximize performance for their dollar, that will be enough. But it's certainly not a very well rounded card if power consumption and noise are factored in.

So, equal performance to Nvidia's competing cards at slightly lower prices (we hope), but at a big cost: far higher power consumption (and thus, I assume, heat?). For gaming, Nvidia is probably still the best choice on virtually every metric, but the interesting thing about Vega is that there's every indication it will do better on other, non-gaming tasks.